Microwave antennas which comprise a desired number of mutually parallel hollow waveguides are well known to the art. The waveguides are disposed in close relationship and are provided on their front sides with a large number of short, sequentially disposed slots through which microwave energy is emitted to the surroundings. The slots are uniformly disposed along the hollow waveguides and extend in the direction of the longitudinal axis thereof. One antenna of this kind is described in the U.S. Pat. No. 4,429,313. According to this patent, the rear side of the waveguide is provided with feed waveguides which extend transversely to the waveguide axis. These feed waveguides are operative to supply the hollow waveguides with microwave energy through coupling slots which extend transversely to the waveguide axis. The feed waveguides are provided with lateral projections and energy is supplied through coaxial lines, the centre conductors of which project into respective projections. When supplying power to large antennas, the microwave energy is distributed through several layers of lattice-laid hollow waveguides. The arrangement is relatively bulky and complicated, which is highly disadvantageous in the case of mobile microwave antennas for instance.
The U.S. Pat. No. 3,524,189 teaches a microwave antenna comprising mutually-parallel, slotted hollow waveguides, as described above. The waveguides may be ridge waveguides, the ridge part of which extends in the direction of the waveguide axis and projects into the waveguide. The waveguide is fed through a coaxial line, the centre conductor of which enters the waveguide at its ridge. Although this arrangement is simple, it can be difficult at times to match the impedance of the coaxial line with that of the hollow waveguide, particularly when the waveguide is a ridge waveguide.